Heating device

ABSTRACT

Device for induction heating of ring-shaped objects, including a magnetizable core with one or several coils, which core has a moveable part that is displaceable, for insertion through the ring-shaped object that is to be heated. The object that is to be heated rests on rails or bars on which the object can slide electrically and thermally insulated. The device is inclined laterally so that the objects that are to be heated can slide in to and/or out from the heating position.

This invention concerns a heating device where the heating is carriedout by means of induction. In particular the invention has as its objectan induction heating that can be used in the connection with hardening;and then in particular to harden rapidly hardening steel that hardens inair. To heat objects by means of induction is in itself well known, butat heating for hardening the demands on the heating device are fargreater when it comes to the achieving of a uniform temperature in theobjects that are to be hardened. If the temperature is not uniformobjects of some types of steel that are to be hardened undergo a changeof shape during the heating, which then remain after the cooling, thisis in particular the case for a new air hardening steel. Furthermore thehardness may vary if the temperature is non-uniform. Since at hardeningof for instance the above new type of steel the temperatures used athardening are very high the steel will be very plastic and easilydeformed and the object or objects that are to be hardened must thereforbe handled very gentle.

In view of the above problems the object of the invention is to achievean induction heating that works very fast, efficiently, uniformly andthat furthermore is very gentle to the objects that are to be heated.

In accordance with the invention this object is solved by placing theobject that is to be heated in an opening in a C-shaped main coresupported on a pole piece. Through the object that is to be heated, inparticular rotationally symmetrically ones, a moveable core connectionis arranged extending straight through this object so that the core isclosed. The object that is to be heated, the core and a coil arrangedaround this constitute principally a transformer where current isinduced in the object that is to be heated. By selecting the amperage inthe coil the energy generation in the object that is to be heated isalso controlled. Since the current in the object is distributed over itscross section the heating will become very uniform. By letting theobject that is to be heated rest on distance means of for instancealuminum oxide transfer of heat energy from the heated object to thecore is eliminated.

The part of the core that extends through the object that is to beheated extends either to the opposite pole piece of the core to contactwith this through recesses in the insulating distance means or isprovided with recesses corresponding to the insulating means. Theinsulating means may either be constituted by an entire surface with oneor several recesses for the contact of the pole piece through thiscoating alternatively one can consider the insulating means beingconstituted by protruding bars or rails on which the object that is tobe heated rests. Recesses are either arranged in the rails for theopposed moveable central core part alternatively groves are shaped inthe downwards facing surface of this in contact with the lower polepiece.

Through the above measure not only an electric insulation of the objectthat is to be heated is achieved that prevent induced current fromleaking, but also heat is prevented from leaking over to the core. Inhis way the heat will become uniform through the object on its upperside as well as on bottom side and the risk of deformation andnon-uniform hardening are eliminated respectively. Through the reductionof the heat loss also the strains of the core are reduced as well as theheat loss to this. In order further to reduce the heat losses to coreand pole pieces the surfaces of these that are facing the object that isto be heated may be polished so that the heat radiation is reflected.

The objects that are to be heated are heated piece by piece and restsduring the heating on the thermally and electrically insulating support.Through the use of rail or bar like means the contact surface is alsoreduced and thereby the possible heat transfer.

If so desired also the core part that extends through the object that isto be heated may be provided with bars and a surface coating ofelectrically and thermally insulating material to prevent contactbetween the core and the heated object.

In order to secure a gentle handling of the objects that are to beheated the core and the support surface respectively of the object thatis to be heated are in a further development of the invention arrangedinclined. In this way the object that is to be heated can when theheating has taken place to a sufficient temperature be released, then toslide away from the place of heating influenced by its own weight to thenext treatment step. The angle of inclination is chosen so that theobject that is to be heated by its own weight slide on the bars.

Further advantages and characteristics of advantageous furtherdevelopments of the inventive thought are apparent from the patentclaims and the following description of a preferred embodiment withreference to the enclosed drawings. In the drawings

FIG. 1 schematically show an installation in accordance with theinvention seen from the side,

FIG. 2 the installation seen from above,

FIG. 3 the heating device in itself seen from the side,

FIG. 4 a detail of the heating device and

FIG. 5 a cross section through the lower pole piece.

The installation for hardening of for instance ball bearing and rollerbearing races include a first heating module 1, a following air coolingmodule 2 and thereafter a tempering module with following cooling tub 4.

The heating module includes a principally C-shaped core that is inclined20 degrees, The lower part in the opening in the core is provided withan exchangeable pole piece 6 that in principle has the shape of a plate.In the plate grooves 7 are cut and in these bars of aluminum oxide arereceived that protrude a few millimeters over the surface of the polepiece. In the opposite part of the core an upper pole piece isconstituted of a central cylindrical displaceable core part 9 soarranged that it can be displaced down to contact with the lower polepiece 6 and respectively be lifted from this a sufficient distance toallow the bearing rings that are to be hardened to pass between the polepieces. This displacement of the displaceable core part 9 takes place bymeans of a motor arranged in the upper end of the core and furthermore alocking device is arranged to fix the moveable cylindrical pole piecepart against the core when heating is carried out, in order to close themagnetic field and reduce the vibration risk. On the core furthermoretwo coils 10, 11 are arranged. The inclined lower pole piece plane isextended with an inclined plane constituted of stainless bars 13extending in the direction of movement of the heated bearing rings downto a belt conveyor 14.

The transporting surface 15 of the belt conveyor is made of stainlesshelixes which at the same time as a satisfactory supporting surfaceprovide a minimal heat transfer and pressure influence. The conveyor 14extends closest to the heating module through a heat trap constituted ofa water cooled jacket 16 that is painted black or coated with some otherheat absorption promoting material. From this the conveyor runs throughan air cooling section where air is blown through with the object tocool the heated goods. The air and water cooled sections can also if sodesired be arranged overlapping that is one may have air channelsthrough the water cooled jacket. Since the conveyor is constituted bystainless helixes also a good air transport is enabled straight throughthis and the bearings that are to be cooled. The air is recirculated inthe air cooling section and is fed through so called iris valves 17 thatindependent of the degree of throttling provide the same shape of theflow. The air is cooled with a water cooled cooling core.

After the air cooling section a check control station 18 follow where aheat camera reads the temperature of the bearing rings. If thetemperature is too low this indicates that the heating has failed andthe ring is pushed off from the band laterally. If three consecutiverings are too cold the feed of rings to the heating device is stoppedfor checking and possible attending. One can proceed in the same waywith too hot rings.

The belt conveyor 14 finally deliver the air hardened rings that thenhave a temperature of 75 to 100° C. in a tub 19 filled with water forfinal cooling to room temperature or below this for completing of thehardening. Since the temperature before the water bath is that low onedoes not risk that the rings cracks or crackles. From the tub 19 therings are transported up with a belt conveyor 20 and are fed to the heatdevice 3 for tempering heating that to its general build coincide withthe first heating device and from this heating device the bearing ringsare after intended heating once again dropped into a water filled tub 4for cooling, wherefrom they are then transported away for furthermachining, that is in particular grinding.

The above described heating device works in such a manner that whenheating is to take place the upper circular pole piece 9 is pulled upand a bearing ring is by means of a robot placed on the lower pole piece6 lying on the bars 8 of aluminum oxide on this. The bearing ring slidesafter being released by the robot down towards two obliquely arrangedbars 21 of stainless steel that extend inward from each side. These barsare electrically insulated from the surrounding but connected to aseparate current source and immediately when a bearing ring is incontact with both of the oblique bars an electric contact is establishedand a current flows through the bars and the ring, which is used as anindication that the ring is in position.

When the bearing ring is in position the upper circular pole piece 9 isthen displaced downwards to contact with the lower pole piece 6. Thebars 8 are left out in the contact area with the lower pole piece. Theupper pole piece is then locked against the main core and current is fedto the coils 11 inducing a powerful current in the bearing ring that ina few seconds reach the required hardening interval of the temperature.At this the bearing ring expands giving a small movement in relation tothe stainless bars 20, 21, which movement also gives a small abrasionensuring electric contact. If so is desired one can also considerallowing a vibrator to vibrate the bars slightly in order to increasethe abrasion and thereby improve the electric contact. Furthermore thevibration may facilitate a possible required lateral movement at anuncentered placing of the bearing rings.

The temperature of the bearing rings is monitored by means of a heatcamera for possible adaption of current and feed tine of the currentthrough the coil.

When the temperature level has been achieved slightly above the lowerlimit of hardening the current to the coil is interrupted, the upperpole piece is released and lifted by its associated motor 22. Thereafterthe heated bearing ring is released by the oblique stainless bars beingpulled apart laterally and the bearing ring slides on the aluminum oxidebars to the conveyor.

By controlling the lateral movements of the two stainless bars 20, 21the rings may be spread somewhat over the width of the conveyor so thatthe rings end up further from each other and thereby reduce the risk ofmutual heat influence, that otherwise at too closely placed rings maylead to a non-uniform cooling process with slower cooling of the partsof the rings that are close to each other.

After the gentle landing of the bearing rings on the conveyor 14 theseenter the area of the water cooled jacket 16. The powerful heatradiation from the bearing rings is absorbed by the jacket and heats thecooling water in this and a reduced amount of the heat that is radiatedout towards the jacket is reflected back towards the rings that therebycan emit heat in about the same rate as if they should be entirely freefrom reflecting environment. The jacket thus makes it possible withefficient cooling in a small space. Also the following air cooling isefficient since the air is water cooled in a cooler 22, for instancewith the same circulating water that is used in the water cooled jacket.Through a fast air exchange also in this a fast, efficient and uniformfurther cooling is achieved.

Also in the following tub for water cooling of the bearing rings thesame cooling water may be used and this may also be used after thetempering if so desired. The cooling water circulates after use to a notshown cooling device where the temperature is lowered, whereafter thecooling water is reused.

The water cooled jacket 16 is located closest to the heating device 1since the heat emitted as radiation is as largest when the rings are thehottest.

In order to make it easier for the rings to slide down from their placeat the heating down towards the conveyor a nozzle for pressurized air ortwo may be arranged on the upper side of these so that an impact ofpressurized air can help to start the rings. In this way the angle ofinclination of the core and the plane on which the rings sliderespectively can be changed, thereby reducing the risk that for instancehigher rings fall over on the conveyor.

For the adaption to bearing rings with different height and diameterrespectively the pole pieces (flat and circular part) when needed caneasily be changed, which further is facilitated by the heating of thepole pieces being very small. In comparison with known hardening methodsthe hardening according to the invention may in a quite different way beinserted into a production line, at which also very quick changesbetween different dimensions are possible.

Advantageously the heating in he heating stations is monitored with heatcameras.

The invention thus enables fast and efficient handling of the hardening,in particular of the new air hardening steel since this need not to bekept hot for a long time but is restructured fast when the correcttemperature interval has been reached, which temperature interval iscomparatively broad. Since the heating can take place uniformly withoutharmful influence on for instance the bottom of the rings a good degreeof uniformity is obtained in each ring as well as from ring to ring.Since the steel in question swell somewhat at hardening a possible lowertemperature on the bottom side would easily result in a slight coneshape. Since this can be avoided a very good precision and symmetry canbe obtained for ready bearing rings, which in turn means that the amountof following grinding work or rather die amount of material that has tobe ground away can be reduced, improving the economy in the manufacture.

Since the heating is effected electrically and the cooling withrecirculating water and recirculating air that in turn is cooled by thewater a very environmental friendly installation is achieved that doesnot emit any pollution to the environment. Since the installation is so“clean” it can be located in direct connection to the rest of themachines for machining without inconveniences for these. Since theinstallation without disadvantage can be built in and be enclosed bypanels respectively it will furthermore be very silent.

1. Device for induction heating of ring shaped objects, wherein amagnetizable core with one or several coils, which core has a moveablepart that is displaceable, for the inserting through the ring shapedobject that is to be heated, the object to be heated resting on asupport that is electrically and thermally insulating.
 2. Deviceaccording to claim 1, wherein the support that is electric and thermallyinsulating and support the object that is to be heated comprise rails orbars on which the object can slide.
 3. Device according to claim 1,wherein the bars have recesses or are left out where the part of thecore that extends through the object that is to be heated can be broughtin contact with the underlying pole piece.
 4. Device according to claim2, wherein recesses are arranged in the moveable core part so that thesecan grip over the slide rails and come in contact with the underlyingpole piece.
 5. Device according to claim 1, wherein it is inclinedlaterally so that objects that are to be heated can slide in to and/orout from the heating position.
 6. Device according to claim 1, whereinthe object that is to be heated is held in place by two angled rods. 7.Device according to claim 6, wherein the angled bars are insulated fromthe surroundings but mutually in contact with an electric sensor thatcan sense when the objects that are to be heated give an electriccontact between the two angled bars.
 8. Device according to claim 7,wherein the rods are of stainless steel and are brought to vibrateslightly.
 9. Device according to claim 1, wherein the preheated objectsafter the heating is fed through a space that is surrounded by a watercooled jacket for the draining of heat.
 10. Device according to claim 1,wherein a nozzle for pressurized air is arranged to blow air towards theheated object when this is to be moved from the heating location.